Control device for internal combustion engine

Abstract

To provide a control device for an internal combustion engine capable of appropriately controlling ignition timing after occurrence of knocking while suppressing deterioration of efficiency.SOLUTION: A combustion chamber-wall temperature estimation unit 501 that obtains an estimated value of a combustion chamber-wall temperature including a combustion chamber-wall surface temperature and a combustion chamber-wall internal temperature, and an ignition timing control unit 502 that performs retardation of an ignition timing and advancement of the ignition timing after the retardation are provided, and the ignition timing control unit 502 sets a retardation amount on the basis of at least the estimated value of the combustion chamber-wall internal temperature in retardation control for performing retardation when a knock is detected.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a control device for an internal combustion engine. [Background technology]

[0002] In recent years, regulations regarding fuel economy and exhaust emissions for automobiles and other vehicles have been strengthened. Such regulations are expected to become even stricter in the future. In particular, regulations regarding fuel economy are an issue of great concern due to the recent rise in fuel prices, the impact on global warming, the depletion of energy resources, and other issues.

[0003] Under these circumstances, for example, in the automotive industry, various technological developments are being made with the aim of improving the fuel economy and exhaust performance of vehicles. One example of the technologies being developed with the aim of improving fuel economy is a high compression ratio technology that increases the compression ratio of an internal combustion engine. Another example of the technologies being developed with the aim of improving exhaust performance is a multi-stage injection technology that injects fuel multiple times during the intake stroke, reducing the amount of fuel injected per injection and thereby reducing the particulate number (PN).

[0004] Incidentally, in the above-mentioned high compression ratio technology, although increasing the compression ratio of an internal combustion engine improves thermal efficiency and fuel economy, it is known that the temperature inside the combustion chamber rises, making knocking (hereinafter sometimes referred to as "knock") more likely to occur. Therefore, in conventional internal combustion engines, knocking is detected by utilizing vibrations of the engine block or an increase in a specific frequency signal level of the in-cylinder pressure when knocking occurs. The occurrence of knocking can be detected, for example, by attaching a vibration-type knock sensor to the engine block and analyzing the signal output from the knock sensor over a predetermined period (knock window) using FFT (Fast Fourier Transform).Conventional internal combustion engines have prevented subsequent knocking by retarding the ignition timing after knocking has occurred based on this detection information.

[0005] As a method for controlling ignition timing to prevent knocking, there is prior art such as that disclosed in Patent Document 1. The technology described in Patent Document 1 uses a means for setting the ignition retard amount for the ignition retard control performed after knock occurs, based on an estimated value of the surface temperature of the combustion chamber wall (hereinafter referred to as surface temperature), which is one of the factors that influence the occurrence of knock. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2022-032184 Summary of the Invention [Problem to be solved by the invention]

[0007] However, it was newly discovered that, for example, when two conditions are assumed in which the surface temperature of the combustion chamber wall is the same but the internal temperature of the combustion chamber wall is different, if the same ignition retard amount is set, the surface temperature after the ignition retard will be different under the two conditions.In other words, with the technology described in Patent Document 1, if the ignition timing manipulation amount, including the ignition retard amount after knocking occurs, is determined based only on the surface temperature, a new problem occurs in that the surface temperature may be cooled excessively or insufficiently.

[0008] The present invention has been made in consideration of this problem, and an object of the present invention is to provide a control device for an internal combustion engine that can appropriately control ignition timing after knocking occurs while suppressing deterioration in efficiency. [Means for solving the problem]

[0009] The control device for an internal combustion engine of the present invention includes a combustion chamber wall temperature estimator that calculates an estimated value of the combustion chamber wall temperature, including the combustion chamber wall surface temperature and the combustion chamber wall internal temperature, and an ignition timing control unit that retards the ignition timing and advances the ignition timing after the retardation. In retard control that retards the ignition timing when knock is detected, the ignition timing control unit sets the retard amount based on at least the estimated value of the combustion chamber wall internal temperature. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a control device for an internal combustion engine that can appropriately control ignition timing after the occurrence of knock while suppressing deterioration in efficiency. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram illustrating an example of a system configuration of an internal combustion engine mounted on an automobile according to a first embodiment of the present invention, together with related configurations. [Figure 2] 1 is a block diagram schematically showing a hardware configuration of an ECU according to a first embodiment of the present invention. [Figure 3] 1 is a schematic view showing a part of a piston and a liner in contact with a combustion chamber of an internal combustion engine according to a first embodiment of the present invention. [Figure 4] FIG. 4 is a diagram showing the time changes in surface temperature and internal temperature when the ignition timing is operated in the first embodiment of the present invention. [Figure 5] FIG. 2 is a functional block diagram showing the processing contents of a combustion chamber temperature estimation and ignition timing control unit in the first embodiment of the present invention. [Figure 6] 4 is a graph schematically showing an ignition timing manipulated variable in the first embodiment of the present invention. [Figure 7] 5 is a flowchart showing the processing contents of a combustion chamber wall temperature estimation unit in the first embodiment of the present invention. [Figure 8] FIG. 3 is a schematic diagram showing a combustion chamber wall transmission rate in the first embodiment of the present invention. [Figure 9] 5 is a flowchart showing the processing performed by a delay amount calculation unit in the first embodiment of the present invention. [Figure 10] FIG. 3 is a schematic diagram showing a map for determining a knock recurrence temperature in the first embodiment of the present invention. [Figure 11]FIG. 3 is a schematic diagram showing a map for determining a retard margin based on the temperature inside the combustion chamber wall or the knock frequency in the first embodiment of the present invention. [Figure 12] 5 is a flowchart showing the processing performed by an advance angle amount calculation unit in the first embodiment of the present invention. [Figure 13] FIG. 3 is a schematic diagram showing a map for determining a retardation margin based on the temperature inside the combustion chamber wall or the knock frequency in the first embodiment of the present invention. [Figure 14] 4 is a chart illustrating an example of a procedure for determining an advance angle amount in the first embodiment of the present invention. [Figure 15] 5 is a flowchart showing the processing performed by an advance angular speed calculation unit in the first embodiment of the present invention. [Figure 16] FIG. 3 is a diagram for explaining the relationship between the convergence time of the ignition timing and the knock frequency in the first embodiment of the present invention. [Figure 17] 1A and 1B are diagrams showing the time change in the operation of ignition timing in the first embodiment of the present invention, where (a) shows the case where the difference between the internal temperature and the surface temperature of the combustion chamber wall is small, and (b) shows the case where the difference between the internal temperature and the surface temperature is large. [Figure 18] 10 is a flowchart showing the processing steps for estimating the temperature of a combustion chamber based on knock intensity and knock frequency in a second embodiment of the present invention. [Figure 19] FIG. 10 is a schematic diagram showing the relationship between knock intensity and surface temperature in a second embodiment of the present invention. [Figure 20] FIG. 10 is a schematic diagram showing the relationship between knock frequency and the difference between the surface temperature and the internal temperature in the second embodiment of the present invention. [Figure 21] 10 is a flowchart showing the processing contents of a delay angle amount calculation unit, an advance angle amount calculation unit, and an advance angular speed calculation unit in the second embodiment of the present invention. [Figure 22] FIG. 10 is a schematic diagram showing a map of the retard amount with the surface temperature and the internal temperature as axes in the second embodiment of the present invention. [Figure 23] FIG. 10 is a schematic diagram showing the difference between the retard amount and the advance amount, with the surface temperature and the internal temperature as axes, in the second embodiment of the present invention. [Figure 24] FIG. 10 is a schematic diagram showing the relationship between the difference between the surface temperature and the internal temperature and the advance angular speed in the second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] An embodiment of the present invention will be described below with reference to the drawings. In this embodiment, an internal combustion engine that is mounted on an automobile or the like and uses gasoline as fuel will be described as an example, but the present invention can also be applied to other internal combustion engines that use different types of fuel, specifications, or uses.

[0013] [First embodiment] First, a first embodiment of the present invention will be described with reference to Figures 1 to 17. Figure 1 is a schematic diagram illustrating an example of the system configuration of an internal combustion engine mounted on an automobile, along with related configurations. The internal combustion engine ENG shown in Figure 1 is a direct-injection internal combustion engine for automobiles that is driven by spark ignition combustion. For simplicity, Figure 1 shows only one of multiple cylinders along with the related configuration. This internal combustion engine ENG employs variable valve timing control (VTC), which continuously adjusts the opening and closing timing of the intake valves according to the engine speed and load.

[0014] The internal combustion engine ENG of this embodiment includes an internal combustion engine body, an intake mechanism, an in-cylinder fuel injection mechanism, an ignition mechanism, an exhaust mechanism, a cooling mechanism, and the like, as well as an ECU (Electronic Control Unit) 100 that controls each part. The ECU 100 is a control device that controls the operation of the internal combustion engine ENG. The ECU 100 calculates and controls the main operating variables of the internal combustion engine ENG, such as the air flow rate, fuel injection amount, ignition timing, and fuel pressure, based on the operating state of the internal combustion engine ENG obtained from output information from various sensors.

[0015] The internal combustion engine body includes an engine block 30, a liner 32 that constitutes the cylinder 14, a piston 33 inside the cylinder 14, a cylinder head 34 at the top of the cylinder 14, and the like. A crank angle sensor 19 is disposed in the crank section to detect the position of the piston 33. The crank angle sensor 19 transmits the detection result (output information) to the ECU 100. The ECU 100 calculates the rotation speed of the internal combustion engine based on the output information of the crank angle sensor 19. Further, a knock sensor 21 is disposed in the engine block 30. The knock sensor 21 is a sensor that detects vibrations of the engine block 30. The knock sensor 21 converts the detected vibrations into an electric signal and transmits it to the ECU 100. The ECU 100 determines whether knocking (abnormal combustion) has occurred based on the intensity of the output signal of the knock sensor 21 from the engine block 30, etc.

[0016] The internal combustion engine ENG includes an accelerator opening sensor 12. The accelerator opening sensor 12 detects the depression amount of the accelerator pedal, that is, the accelerator opening. The accelerator opening sensor 12 transmits the detection result (output information) to the ECU 100. The ECU 100 calculates the required torque based on the output information from the accelerator opening sensor 12. That is, the accelerator opening sensor 12 can also be said to be a required torque detection sensor that detects the torque required for the internal combustion engine ENG.

[0017] The intake mechanism supplies air to a plurality of cylinders and includes an air flow sensor (AFS) 1, an intake pressure sensor (MAP) 3, and an intake pipe 7 having a collector 6. The air flow sensor 1 measures the intake air amount (air flow rate) and intake air temperature. The intake pressure sensor 3 measures the intake pipe pressure (intake pressure). The various sensors such as the air flow sensor 1 and the intake pressure sensor 3 transmit their detection results to the ECU 100.

[0018] The ECU 100 calculates the throttle opening and sends the calculated throttle opening as a throttle drive signal to the electronically controlled throttle 2. The electronically controlled throttle 2 adjusts the intake pipe pressure (in other words, the air flow rate). The cylinder head 34 is provided with a variable valve 5 for adjusting the air-fuel mixture flowing into the cylinder or the exhaust gas discharged from the cylinder. The variable valve 5 adjusts the intake amount and internal EGR amount for each cylinder.

[0019] The in-cylinder fuel injection mechanism includes a fuel injection device (hereinafter also referred to as an injector) 13 for each cylinder, which directly injects gasoline fuel into each of the cylinders. A high-pressure fuel pump (not shown) and a fuel pipe (not shown) are connected to the injector 13 for supplying high-pressure fuel. A fuel pressure sensor for measuring the fuel injection pressure is provided in the fuel pipe, and the detection result (output information) of the fuel pressure sensor is sent to the ECU 100. The fuel injection amount calculated by the ECU 100 is converted into a valve-opening pulse signal and sent to the injector 13.

[0020] The ignition mechanism includes an ignition coil 16 for igniting a mixture of gasoline fuel and air injected into the cylinder, and an ignition plug 17 for supplying ignition energy to the ignition coil 16 for each cylinder. In the ignition mechanism of this embodiment, the ignition timing is controlled by the ECU 100. An ignition signal is sent to the ignition coil 16 so that ignition occurs at the ignition timing controlled by the ECU 100. When the ignition signal is sent from the ECU 100 to the ignition coil 16, the air-fuel mixture is combusted in the cylinder.

[0021] The exhaust mechanism includes an exhaust pipe 15 that exhausts the air after combustion inside the cylinder. The exhaust pipe 15 includes a three-way catalyst 10 that purifies the exhaust, and an air-fuel ratio sensor 9 that detects the air-fuel ratio of the exhaust gas. The air-fuel ratio sensor 9 transmits the detection result (output information) to the ECU 100. An external EGR unit 24 is provided downstream of the three-way catalyst 10 between the three-way catalyst 10 and the intake pipe 7.

[0022] The cooling mechanism includes a cooling water system (not shown) for lowering the temperatures of the engine block 30, liner 32, cylinder head 34, etc., and an oil jet system 20 for lowering the temperatures of the piston 33, crank, etc. The oil jet system 20 is connected to a variable displacement (variable oil pressure) oil pump 20a.

[0023] The cooling mechanism includes a temperature sensor 18 that measures the temperature of the coolant circulating around the internal combustion engine ENG. The temperature sensor 18 transmits the detection result (output information) to the ECU 100. The oil pump 20a also adjusts the output (flow rate, oil pressure) to adjust the amount of oil injected from the oil jet system 20 toward the back of the piston 33 of each cylinder.

[0024] In such an internal combustion engine ENG, fuel injected from an injector 13 is added to air that flows into a cylinder 14 from an intake pipe 7 via an intake valve to form an air-fuel mixture. The air-fuel mixture is ignited (exploded) by a spark generated by a spark plug 17 at a predetermined ignition timing. The combustion pressure of the air-fuel mixture then pushes the piston downward, rotating a rotating shaft (crankshaft) connected to the piston via a connecting rod. This generates driving force for the internal combustion engine ENG. The exhaust gas after the explosion is sent to the three-way catalyst 10 via an exhaust pipe 15. The exhaust gas is purified in the three-way catalyst 10 and then discharged to the outside.

[0025] FIG. 2 is a block diagram showing a schematic hardware configuration of the ECU 100. As shown in FIG. 2, information from various sensors etc. is input to an input circuit 121 of an ECU 100, which is a control device for an internal combustion engine ENG. The information input to the input circuit 121 includes the following information. Air flow rate (intake flow rate) from air flow sensor 1, Intake pipe pressure (intake pressure) from intake pressure sensor 3, - the coil primary or secondary voltage from the voltage sensor of the ignition coil 16; the fuel injection pressure from the fuel pressure sensor of the fuel injector 13; the crank angle from the crank angle sensor 19; The air-fuel ratio of the exhaust gas from the air-fuel ratio sensor 9 (exhaust air-fuel ratio), the temperature of the cooling water from the temperature sensor 18, -Accelerator opening from accelerator opening sensor 12, - Rotational speed of the rotating shaft (crankshaft), Various VTC setting values ​​(VTC settings), Knock sensor signals, etc. The information input to the ECU 100 is not limited to the above.

[0026] Information input to the input circuit 121 of the ECU 100 is sent to the input port side of the input / output port 122. The input information sent to the input / output port 122 is temporarily stored in the RAM 123c and is processed in the CPU 123a according to a predetermined control program. The control program describing the content of the processing is written in advance in the ROM 123b. Input information is calculated according to the control program, and output information for controlling the internal combustion engine ENG is generated.

[0027] Output information indicating the amount of actuation of the ignition coil 16 is temporarily stored in the RAM 123c, and then sent to the output port side of the input / output port 122, and then sent to the ignition control unit 124, fuel injection control unit 125, and the like. It should be noted that various actuators other than those mentioned above are used in the internal combustion engine ENG, but a description thereof will be omitted here.

[0028] In this embodiment, the ECU 100 has an ignition control unit 124 as a drive circuit. The ignition control unit 124 acquires information (operation amount) relating to the timing and duration of energization of the ignition coil 16 as the operation amount of the associated actuator. The ignition control unit 124 controls the timing and duration of energization of the ignition coil 16 based on the acquired operation amount. In this embodiment, a part of the ignition control unit 124 for controlling the time for which the ignition coil is energized and the amount of discharge energy may be implemented in a device separate from the ECU 100.

[0029] Next, heat transfer in the combustion chamber wall of the internal combustion engine ENG will be described. FIG. 3 is a schematic diagram showing a part of the combustion chamber wall in contact with the combustion chamber. The combustion chamber 31 is a space where a mixture of fuel and air is burned, and the walls in contact with the combustion chamber 31 are the combustion chamber walls. The combustion chamber walls shown in FIG. 3 are a liner 32, a piston 33, and a cylinder head 34.

[0030] The surfaces of the combustion chamber wall are surfaces 32a, 33a, and 34a of the liner 32, piston 33, and head 34. The surfaces 32a, 33a, and 34a are the surfaces that come into contact with gas inside the combustion chamber 31. Furthermore, the interior of the combustion chamber wall is the interiors 32b, 33b, and 34b of the liner 32, piston 33, and head 34. The combustion chamber wall is usually in contact with cooling water, air, oil jets, etc. on the side opposite to the combustion chamber side (back side). The temperature of the combustion chamber wall is controlled by exchanging energy with these through heat transfer.

[0031] The temperature inside the combustion chamber wall changes more slowly than the temperature on the surface of the combustion chamber wall due to the heat capacity of the combustion chamber wall and the heat transfer and heat exchange with the back side. On the other hand, the temperature of the surface of the combustion chamber wall tends to change more easily in response to changes in the conditions of the combustion chamber 31 than does the temperature change inside the combustion chamber wall. This difference in response results in a situation where the internal temperature of the combustion chamber wall is different even though the surface temperature is the same.

[0032] In Figure 4, the upper part shows a signal that detects whether or not knock has occurred (hereinafter referred to as the knock flag), the middle part shows the operation of the ignition timing, and the lower part shows the change in combustion chamber wall temperature over time when the ignition timing is operated. Figure 4 shows examples of combustion chamber wall temperatures under two conditions. Under the two conditions, Condition L and Condition H, the surface temperature when knock occurs is the same, but the internal temperature when knock occurs is higher under Condition H than under Condition L.

[0033] As shown in the middle part of FIG. 4, the history of the surface temperature Tsf and the internal temperature Tin when the same ignition timing operation is performed under each of the conditions L and H is shown in the bottom part of FIG. The change in combustion chamber wall temperature in the lower part of Figure 4 is shown by the solid lines for the surface temperature TsfL and the internal temperature TinL under condition L, and the dashed lines for the surface temperature TsfH and the internal temperature TinH under condition H.

[0034] The two dashed lines in the lower row indicate the steady-state values ​​of the surface temperature Tsf and the internal temperature Tin that are reached when the ignition timing is maintained at ADV1 and a constant rotation speed is continued. On the horizontal axis, t1 indicates the timing when knock occurred, and t2 indicates the timing when the ignition timing was retarded. t3 indicates the timing when the ignition timing was advanced after being retarded, returning it to the ignition timing before knock occurred. t4 indicates the timing when the surface temperature TsfH under condition H nearly converged to a steady-state value. t5 indicates the timing when the surface temperature TsfL under condition L converged.

[0035] In Figure 4, the ignition timing at the time t1 when the knock occurs is set to ADV1, and after the knock occurs the ignition timing is temporarily retarded, and then gradually advanced back to the original ignition timing ADV1, and the ignition timing is controlled so that the ignition timing ADV1 is maintained. After knock occurs at time t1, if the ignition timing is retarded at time t2, which is the next combustion cycle, the amount of heat transferred from the gas in the combustion chamber 31 to the surfaces (32a, 33a, 34a) of the combustion chamber walls (liner 32, piston 33, and head 34) decreases, and the surface temperatures TsfL and TsfH decrease.

[0036] On the other hand, when the amount of heat conduction to the interior (32b, 33b, 34b) decreases due to a decrease in the surface temperatures TsfL and TsfH, the internal temperatures TinL and TinH decrease. Therefore, the decrease in the internal temperatures TinL and TinH occurs later than the decrease in the surface temperatures TsfL and TsfH.

[0037] Under condition H, where the internal temperature is high, the amount of heat conducted to the interior of the combustion chamber wall is smaller than under condition L. As a result, as shown by A in the figure, the decrease in surface temperature TsfH after retarding the ignition timing is smaller than under condition L. Thereafter, by advancing the ignition timing, the amount of heat transferred from the combustion gas in the combustion chamber to the surface of the combustion chamber wall increases, causing the surface temperatures TsfL and TsfH to increase, and after a slight delay, the internal temperatures TinL and TinH also increase.

[0038] As shown in the middle part of Figure 4, if the ignition timing is advanced at a predetermined rate over multiple combustion cycles, and then the original ignition timing ADV1 is restored and operation is continued at a constant value, the internal temperatures TinL and TinH will eventually converge to a steady state. The state in which the internal temperature TinH drops after the retard operation under condition H is closer to this steady state than the internal temperature TinL under condition L. Therefore, condition H converges to the steady state at time t4, earlier than condition L. On the other hand, condition L converges to the steady state at time t5, later than condition H. This difference in convergence time is indicated by B in the figure.

[0039] In this way, even if the surface temperatures TsfL and TsfH are the same at the time that knock occurs, if the internal temperatures TinL and TinH are different, the change in surface temperature in response to the operation of the ignition timing will differ. Therefore, the control device for the internal combustion engine ENG of this embodiment controls the ignition timing taking into account not only the surface temperature of the combustion chamber wall but also the internal temperature, thereby suppressing knocking while preventing a deterioration in efficiency such as fuel economy and output.

[0040] FIG. 5 is a functional block diagram showing the processing contents of the combustion chamber wall temperature estimation unit and the ignition timing control unit in the CPU. The combustion chamber wall temperature estimation unit 501 and the ignition timing control unit 502 are functions realized by a program executed by the CPU 123a in the ECU 100. The CPU 123a performs arithmetic processing using various inputs from the input circuit 121. For example, the inflow air flow rate of each cylinder is calculated using input values ​​such as an air flow sensor measurement value, engine speed, and coolant temperature. The pressure of the intake air is calculated based on the mass within the volume from the throttle to the engine and other factors using the energy conservation equation and the gas state equation.

[0041] The combustion chamber wall temperature estimation unit 501 shown in FIG. 5 estimates the combustion chamber wall temperature, including the combustion chamber wall surface temperature and the combustion chamber internal temperature, based on the operating condition parameters, temperature condition parameters, ignition timing, etc., when knock occurs and during various assumed times. Ignition timing control section 502 controls the ignition timing using the estimated surface temperature and internal temperature of the combustion chamber wall when knocking occurs and when various other conditions are assumed.

[0042] The ignition timing control unit 502 performs retard control to retard the ignition timing, and advance control to advance the ignition timing immediately after the retard control. The ignition timing control unit 502 of this embodiment may perform advance control all at once immediately after the retard control, or may perform advance control by dividing it into first advance control and second advance control that advances the ignition timing at an advance speed slower than that of the first advance control.

[0043] The ignition timing control unit 502 includes a retard amount calculation unit 503 , an advance amount calculation unit 504 , and an advance speed calculation unit 505 . The retard angle calculation unit 503 calculates the retard angle in retard angle control after knock detection. The advance angle calculation unit 504 calculates the advance angle amount after the ignition retard implemented after knock detection, that is, the advance angle amount in the first advance angle control. An advance angle speed calculation unit 505 calculates the speed (advance angle speed) at which the ignition timing is advanced after the ignition advance angle in the first advance angle control, that is, the advance angle speed in the second advance angle control.

[0044] FIG. 6 is a chart for explaining the amount of operation of the ignition timing. The knock flag shown in the upper part of Fig. 6 indicates whether or not knock has occurred. The lower part of Fig. 6 shows the change in ignition timing over time when ignition timing is controlled using the retard amount, advance amount, and advance rate calculated by combustion chamber wall temperature estimation unit 501 and ignition timing control unit 502 in Fig. 5.

[0045] When the ignition timing control unit 502 detects the occurrence of knock, it performs retard control to retard the ignition timing using the estimated values ​​of the surface temperature and internal temperature of the combustion chamber wall estimated by the combustion chamber wall temperature estimation unit 501. Here, the retard amount indicates how much the ignition timing is retarded relative to the ignition timing at the time of the knock occurrence or a preset reference ignition timing. This retard amount is an amount by which the ignition timing is rapidly retarded in a short combustion cycle immediately after the knock occurrence. For example, it may be the retard amount in the next combustion cycle immediately after the knock occurrence.

[0046] After performing the retard control, the ignition timing control unit 502 performs a first advance control of the ignition timing. The advance amount indicates how much the ignition timing is advanced relative to the ignition timing that was retarded after the occurrence of knock. This advance amount is the amount advanced in a predetermined short combustion cycle immediately after the retard control of the ignition timing. For example, it may be the advance amount in the next combustion cycle immediately after the retard control. This advance amount is preferably equal to or smaller than the retard amount in the retard control, and in this embodiment, it is an angle smaller than the retard amount in the retard control.

[0047] After the first advance control is performed, if there is room to advance the ignition timing, for example, if the advance amount is smaller than the delay amount in the delay control, a second advance control is performed to gradually advance the ignition timing at an advance speed slower than that of the first advance control. Here, the advance speed can be expressed as the amount by which the ignition timing is gradually advanced per unit time. For example, the advance speed may be the amount by which the ignition timing is advanced over a predetermined number of combustion cycles immediately after the first advance control.

[0048] In this embodiment, the sum of the advance angle amounts in the first advance angle control and the second advance angle control may be set to be equal to the delay angle amount in the delay angle control. By setting in this manner, the first advance angle control and the second advance angle control return the ignition timing to the value before the delay angle control, such as the ignition timing at the time when knocking occurs or a preset reference ignition timing.

[0049] Next, we will explain the process of operating the ignition timing by calculation in the control device for the internal combustion engine ENG. First, a combustion chamber wall temperature estimation unit 501 estimates the combustion chamber wall surface temperature and the combustion chamber wall internal temperature, and then an ignition timing control unit 502 controls the ignition timing based on the estimated values.

[0050] FIG. 7 is a flowchart showing the processing performed by the combustion chamber wall temperature estimation unit. In step S701, the combustion chamber wall temperature estimation unit 501 calculates the amount of energy dQinput / dt [J / s] to be input to the engine. For example, as shown in equation 1, the amount of energy can be calculated using the air flow rate mair [kg / s] detected by the air flow sensor 1, the exhaust air-fuel ratio AbF [-] detected by the air-fuel ratio sensor 9, and the calorific value of the fuel Qfuel [J / kg].

[0051]

number

[0052] After calculating the amount of energy to be input, the process of the combustion chamber wall temperature estimation unit 501 proceeds to step S702. In step S702, the combustion chamber wall temperature estimation unit 501 calculates the energy transfer rate dQwall / dt [J / s] due to heat transfer to the combustion chamber wall using the ignition timing. For example, as shown in equation 2, the energy transfer rate can be calculated using the ratio of the amount of energy transferred to the combustion chamber wall from the amount of input energy (combustion chamber wall transfer rate) Rwall [-].

[0053]

number

[0054] Here, the combustion chamber wall transmission rate Rwall changes continuously depending on the ignition timing. FIG. 8 is a graph that schematically shows the combustion chamber wall transfer fraction. As shown in FIG. 8, when the ignition timing is retarded, the combustion chamber wall transfer fraction decreases from the optimum ignition timing (MBT in the figure). In this case, the combustion chamber wall transfer fraction can be evaluated as a function of the ignition timing. In FIG. 8, the combustion chamber wall transfer fraction can be expressed as a quadratic function of the ignition timing, as shown in equation 3, for example.

[0055]

number

[0056] In step S702, once the energy transfer rate dQwall / dt due to heat transfer to the surface of the combustion chamber wall has been calculated, the processing of the combustion chamber wall temperature estimation unit 501 proceeds to step S703. In step S703, the combustion chamber wall temperature estimation unit 501 calculates the rate of energy transfer due to heat conduction between the surface of the combustion chamber wall and the interior of the combustion chamber wall, where the walls are in contact with each other. The calculation formulas for the rate of energy transfer due to heat conduction can be generalized as the following formulas 4 to 7.

[0057]

number

number

number

number

[0058] In equations 4 to 7, dQsfc / dt is the rate of energy transfer due to heat conduction between the surface of the combustion chamber wall and the wall it comes into contact with [J / s], and dQinc / dt is the rate of energy transfer due to heat conduction between the interior of the combustion chamber wall and the wall it comes into contact with [J / s]. Here, heat conduction is calculated assuming that the combustion chamber wall consists of two walls, the surface and the interior. i is the number assigned to the contacting wall (i=1,2,...). As for the i-th wall, one of the i-th walls relative to the surface is the interior, and conversely, one of the i-th walls relative to the interior is the surface.

[0059] In addition, in equations 4 to 7, dQsfc,i / dt is the energy transfer rate by heat conduction to the i-th wall that the surface contacts [J / s], and dQinc,i / dt is the energy transfer rate by heat conduction to the i-th wall that the interior contacts [J / s]. λsf,i is the thermal conduction coefficient between the i-th wall and the surface [W / m2 / K], λin,i is the thermal conduction coefficient between the i-th wall and the interior [W / m2 / K], Ti is the temperature of the i-th wall [K], Tsf is the temperature of the surface [K], Tin is the temperature of the interior [K], Lsf,i is the distance between the surface and the i-th wall [m], Lin,i is the distance between the interior and the i-th wall [m], Ssf,i is the contact area between the surface and the i-th wall [m2], and Sin,i is the contact area between the interior and the i-th wall [m2].

[0060] 3, examples of walls that come into contact with the surface 32a of the liner 32 include the interior 32b of the liner 32, the surface 33a of the piston 33, the interior 33b of the piston 33, and the surface 34a of the head 34. Examples of walls that come into contact with the interior 32b of the liner 32 include the surface 32a of the liner 32. Similarly, examples of walls that come into contact with the surface 34a of the head 34 include the interior 34b of the head 34 and the surface 32a of the liner 32, and examples of walls that come into contact with the interior 34b of the head 34 include the surface 34a of the head 34. Furthermore, examples of walls that come into contact with the surface 33a of the piston 33 include the interior 33b of the piston 33 and the surface 32a of the liner 32, and examples of walls that come into contact with the interior 33b of the piston 33 include the surface 33a of the piston 33 and the surface 32a of the liner 32.

[0061] The thermal conductivity coefficient, wall distance, and contact area are often determined by physical properties and design values. However, if they cannot be determined from physical properties and design values ​​because multiple materials are sandwiched in the contact area or the shape is complex, appropriate values ​​determined in advance through prior experiments or simulations can be used.

[0062] Once the energy transfer rate due to heat conduction has been calculated in step S703, the processing of the combustion chamber wall temperature estimation unit 501 proceeds to step S704. In step S704, the energy transfer rate due to heat transfer between the inside of the combustion chamber wall and the fluid in contact with the inside is calculated. The fluid in contact with the inside of the combustion chamber wall is, for example, the cooling water, oil jet, or air shown in Figure 3. The formula for calculating the energy transfer rate due to heat transfer can be generalized as the following equations 8 and 9.

[0063]

number

number

[0064] Here, dQint / dt [J / s] is the rate of energy transfer due to heat transfer between the interior and the fluid. i is the number assigned to the contacting fluid (i=1, 2, . . .). Examples of fluids that come into contact with the interior of the liner include cooling water and air. Examples of fluids that come into contact with the interior of the piston include oil jets and air. Examples of fluids that come into contact with the interior of the head include cooling water and air.

[0065] In equations 8 and 9, dQint,i / dt is the energy transfer rate due to heat transfer between the interior and the i-th fluid with which it is in contact. hint,i is the heat transfer coefficient [W / m2 / K] between the interior and the i-th fluid, Tl,i is the temperature of the i-th fluid, and Sinl,i is the contact area between the interior and the i-th fluid. If the heat transfer coefficient and contact area cannot be determined from the physical property values ​​and design values, appropriate values ​​obtained in advance through prior experiments or simulations can also be used.

[0066] In step S704, once the rate of energy transfer due to heat transfer between the interior and the fluid has been calculated, the processing of the combustion chamber wall temperature estimation unit 501 proceeds to step S705. In step S705, the combustion chamber wall temperature estimation unit 501 obtains an estimated surface temperature value and an estimated internal temperature value of the combustion chamber wall using the following equations (10) and (11).

[0067]

number

number

[0068] where Tsf,now is the current estimated surface temperature [K], Tin,now is the current estimated internal temperature [K], Msf is the surface mass [kg], Min is the internal mass [kg], Csf is the surface specific heat [J / kg / K], Cin is the internal specific heat [J / kg / K], and Δt is the calculation period [s]. If the mass and specific heat cannot be determined from the physical property values ​​and design values, appropriate values ​​obtained in advance through prior experiments or simulations can also be used.

[0069] Next, a description will be given of the processing in the ignition timing control unit 502. The processing in the ignition timing control unit 502 includes a delay amount calculation unit 503 calculating the delay amount, a lead amount calculation unit 504 calculating the lead amount, and a lead speed calculation unit 505 calculating the lead speed.

[0070] First, a description will be given of the calculation process of the delay amount by the delay amount calculation section 503. Fig. 9 is a flowchart showing the process performed by the delay amount calculation section. In step S901, retard amount calculation unit 503 sets a target surface temperature decrease amount based on knock recurrence temperature Tkc. Retard amount calculation unit 503 may start processing when the estimated surface temperature reaches a predetermined temperature. In this embodiment, retard amount calculation unit 503 can start processing when the estimated surface temperature reaches a temperature that is obtained by adding a margin to knock recurrence temperature Tkc, which will be described later.

[0071] Here, the knock recurrence temperature Tkc is a reference temperature at which knock is expected to occur, or in other words, the expected knock occurrence temperature. This knock recurrence temperature Tkc is a parameter that can be determined in advance. The knock recurrence temperature Tkc may be calculated assuming a standard fuel. Furthermore, the retard amount and the advance amount (described later) may be calculated based on fuel properties determined based on at least one of a fuel injection parameter and the ratio of the fuel amount to the air amount that results in a stoichiometric mixture ratio.

[0072] The knock recurrence temperature Tkc may be a value that is determined by using a map that is obtained in advance through experiments, simulations, or the like. For example, since the knock recurrence temperature Tkc varies depending on the engine speed, engine load, and coolant temperature, a map based on these factors may be stored in advance, and the appropriate value may be used when calculating the retard amount.

[0073] FIG. 10 is a schematic diagram showing a map of knock recurrence temperature with engine load and engine speed as axes, and each solid line indicates knock recurrence temperature Tkc. Because this relationship varies depending on the coolant temperature, in this embodiment, a map like the one in FIG. 10 is created for each coolant temperature. In this map, the higher the engine speed, the higher the knock recurrence temperature Tkc, and the higher the engine load, the higher the knock recurrence temperature Tkc. Furthermore, the higher the coolant temperature, the higher the knock recurrence temperature Tkc.

[0074] Using the knock recurrence temperature Tkc obtained from the map, the target temperature decrease amount ΔTsf[K] can be determined from the current value Tsf,now of the estimated surface temperature as shown in Equation 12.

[0075]

number

[0076] Here, ΔTsf,mar is a retard margin [K] provided between the temperature reached when the combustion chamber is retarded and the knock recurrence temperature. In this embodiment, the retard margin may be a preset constant value, but it can also be set according to the internal temperature of the combustion chamber wall or the knock frequency. The knock frequency, which will be described later, is the number of knock occurrences per combustion cycle calculated based on the number of knocks that occurred in the immediately preceding predetermined number of combustion cycles. In this embodiment, as will be described later, the knock frequency may be calculated from a value weighted using a weighted average of a single knock flag.

[0077] FIG. 11 is a schematic diagram showing a map for determining the retardation margin based on the temperature inside the combustion chamber wall or the knock frequency. It is assumed that the surface temperature of the combustion chamber wall is difficult to decrease when the internal temperature is high and when the knock frequency is high. Therefore, the retard amount calculation unit 503 can calculate the retard margin ΔTsf,mar using a map that indicates the retard margin corresponding to the estimated internal temperature or the knock frequency. These maps can be set in advance through prior experiments or simulations.

[0078] Once the target surface temperature decrease amount is determined in step S901, the process of the delay amount calculation unit 503 proceeds to step S902. In step S902, the retardation amount calculation unit 503 determines the retardation target surface temperature from the target surface temperature decrease amount and the surface temperature estimate value. For example, the retardation target surface temperature can be calculated from the current value Tsf,now of the surface temperature estimate value and the target temperature decrease amount ΔTsf using Equation 13.

[0079]

number

[0080] where Tsf,tar is the retard target surface temperature [K]. Once the retard angle target surface temperature is determined in step S902, the process of the retard angle amount calculation unit 503 proceeds to step S903.

[0081] In step S903, the retard amount calculation unit 503 sets the retard target ignition timing based on the retard target surface temperature, the estimated surface temperature, and the estimated internal temperature. The retard target ignition timing can be set using, for example, Equation 14, which is derived using Equations 1 to 11.

[0082]

number

[0083] Here, θtar is the retarded target ignition timing [deg], θref is the coefficient [deg] of Equation 3, Tsf,tar is the target value of the surface temperature [K], Tsf,now is the current value of the estimated surface temperature [K], and Ti,now is the current value of the estimated temperature of the i-th wall that the surface contacts [K], and one of the i-th walls is the interior.

[0084] Once the retarded target ignition timing is determined in step S903, the process of the retard amount calculation unit 503 proceeds to step S904. In step S904, the retard amount calculation unit 503 calculates the retard amount from the current ignition timing and the retard target ignition timing. If the current ignition timing is θnow, the retard amount ΔθR can be calculated using equation (15).

[0085]

number

[0086] In setting the retard amount as described above, the ignition timing retard amount is determined taking into account the current estimated value of the temperature inside the combustion chamber wall, as shown in Equation 14. For example, the internal estimated value is taken into account as the current estimated value of the temperature of the i-th wall in contact with the surface. Furthermore, as shown in Figure 11, the higher the estimated internal temperature, the smaller the difference between the internal temperature and the surface temperature, making it more difficult for the surface temperature to drop, and therefore the retard margin is set to be larger. As a result, the ignition timing can be determined so as to satisfy the target surface temperature, taking into account the estimated internal temperature, and therefore an appropriate ignition retard amount can be set.

[0087] Next, the calculation process of the advance angle amount by advance angle amount calculation section 504 will be described. FIG. 12 is a flowchart showing the processing performed by the advance angle calculation unit. In step S1201, advance angle calculation unit 504 compares the current estimated surface temperature value with the knock recurrence temperature. If the current estimated surface temperature value is higher than the knock recurrence temperature, this indicates that the ignition timing retard amount may be insufficient. If the determination is YES, advance angle calculation unit 504 proceeds to step S1205. If the determination is NO, advance angle calculation unit 504 proceeds to step S1202.

[0088] In step S1202, advance amount calculation unit 504 sets an advance target surface temperature with a margin from the knock recurrence temperature. For example, advance target surface temperature Tsf,tar,a can be set using Expression 16 as a value with a margin from the knock recurrence temperature.

[0089]

number

[0090] Here, Tkc is the knock recurrence temperature, and ΔTsf,a is the advance margin [K] that is maintained between the temperature reached when the engine is advanced and the knock recurrence temperature. In this embodiment, the advance margin ΔTsf,a may be a preset constant value, or may be set in accordance with the internal temperature of the combustion chamber wall or the knock frequency. The knock frequency, which will be described later, is the number of knock occurrences per combustion cycle calculated based on the number of knocks that occurred in a predetermined number of immediately preceding combustion cycles. In this embodiment, as will be described later, the knock frequency may be calculated from a weighted value obtained by using a weighted average of a single knock flag.

[0091] FIG. 13 is a schematic diagram showing a map for determining the advance margin based on the temperature inside the combustion chamber wall or the knock frequency. It is assumed that the surface temperature of the combustion chamber wall is difficult to decrease when the internal temperature is high. This also suggests that the surface temperature of the combustion chamber wall is difficult to decrease when the knock frequency is high. Therefore, the advance amount calculation unit 504 can calculate the advance margin ΔTsf,a using a map that indicates the advance margin corresponding to the estimated internal temperature value or the knock frequency. These maps can be set in advance through prior experiments or simulations.

[0092] After the target surface temperature is determined in step S1202, the process of advance angle calculation unit 504 proceeds to step S1203. In step S1203, advance angle calculation unit 504 sets the target ignition timing based on the target surface temperature, the estimated surface temperature value, and the estimated internal temperature value. For example, this can be determined by equation 17, which is similar to equation 14, which is derived from equations 1 to 11.

[0093]

number

[0094] Once the target ignition timing is set in step S1203, the process of the advance angle calculation unit 504 proceeds to step S1204. In step S1204, the advance amount is calculated from the current ignition timing and the target ignition timing using equation 18. For example, it can be calculated from the current ignition timing and the target ignition timing after the advance calculated in step S1003.

[0095]

number

[0096] In this embodiment, instead of steps S1203 and S1204, the target value of the advance angle can be searched for by repeatedly calculating the surface temperature attainment values ​​for a plurality of advance angles.

[0097] Fig. 14 is a chart illustrating an example of a procedure for determining the amount of advance. In Fig. 14, the knock recurrence temperature Tkc is indicated by a solid line, and the target surface temperature value Tsf,tar,a to which the advance margin ΔTsf,a is added is indicated by a dashed line. In step S1203, advance amount calculation unit 504 calculates the surface temperature target values ​​Tsfθ1···Tsfθn for multiple advance amounts for the ignition retard amount after retardation performed by retard amount calculation unit 503. An advance amount is searched for such that the target temperatures Tsfθ1···Tsfθn for each calculated advance amount are temperatures suitable for the current conditions.

[0098] The temperature reached when the spark advance is different when the internal temperature is TinL and when it is TinH, which is higher than TinL. When the internal temperature is TinH, that is, when the difference between the internal temperature and the surface temperature is small, the target surface temperature is reached with a small amount of spark advance. Therefore, the target ignition timing θtar,a varies depending on the difference between the internal temperature and the surface temperature. Therefore, the target ignition timing θtar,a can be determined by finding the advance amount that will result in the surface temperature reached by multiple advance amounts at the current internal temperature being the target surface temperature value (dashed line) with an advance margin.

[0099] On the other hand, if it is determined in step S1202 that the cooling is insufficient, then in step S1205, the amount of ignition advance is set so as to retard the predetermined value, as shown in the following equation (19).

[0100]

number

[0101] As described above, by setting the amount of ignition advance, it is possible to advance the ignition within a range that prevents the surface temperature from exceeding a predetermined value, and by taking the internal temperature into consideration, it is possible to avoid over- or under-advancing the ignition timing. As a result, the period during which the ignition timing is retarded can be minimized, and deterioration in fuel economy due to continued ignition timing retardation can be suppressed.

[0102] Next, the calculation process of the advance angular velocity by the advance angular velocity calculation section 505 will be described. FIG. 15 is a flowchart showing the processing contents of the advance angular speed calculation unit 505. In step S1501, advance angular speed calculation unit 505 calculates the amount of change in the amount of heat conduction based on the estimated value of the surface temperature of the combustion chamber wall and the estimated value of the internal temperature. The energy transfer rate due to heat conduction between the surface and internal of the combustion chamber wall can be expressed as the following equation 20 from equations 4 to 7.

[0103]

number

[0104] Here, dQcinsf / dt is the rate of energy transfer by heat conduction from the surface to the interior [J / s], λinsf is the thermal conductivity between the surface and the interior [W / m2 / K], Tsf is the estimated surface temperature [K], Tin is the estimated internal temperature [K], Linsf is the distance between the surface and the interior [m], and Sinsf is the contact area between the surface and the interior [m2].

[0105] The amount of change in the rate of energy transfer due to thermal conduction can be calculated, for example, by using the current values ​​of Tin and Tsf and the values ​​from several steps ago using Equation 21.

[0106]

number

[0107] Here, ΔdQcinsf / dt is the amount of change in the energy transfer rate due to heat conduction [J / s], dQcinsf / dt(tnow) is the amount of change in the energy transfer rate due to heat conduction [J / s] calculated by inputting the current estimated surface temperature and estimated internal temperature values ​​into equation 20, and dQcinsf / dt(tpast) is the amount of change in the energy transfer rate due to heat conduction [J / s] calculated by inputting the past estimated surface temperature and estimated internal temperature values ​​into equation 20.

[0108] After calculating the amount of change in the energy transfer rate due to heat conduction in step S1501, the processing of the advance angular speed calculation unit 505 proceeds to step S1502. In step S1502, the advance angular speed calculation unit 505 calculates the energy transfer rate by heat transfer from the gas in the combustion chamber to the surface of the combustion chamber wall, which is required to maintain the surface temperature.

[0109] The advance angular velocity calculation unit 505 can calculate the required energy transfer velocity, for example, by calculating the energy transfer velocity due to heat conduction from the gas in the combustion chamber to the surface of the combustion chamber wall at the current ignition timing using equations 2 and 3, and adding this to the change in the energy transfer velocity due to heat conduction calculated in step S1501 using equation 22.

[0110]

number

[0111] Here, dQwall,tar / dt is the energy transfer rate [J / s] by heat transfer from the gas in the combustion chamber to the surface of the combustion chamber wall required to maintain the surface temperature. dQwall,now / dt is the energy transfer rate [J / s] due to heat transfer from the gas in the combustion chamber to the surface of the combustion chamber wall, calculated from Equation 2 and Equation 3 and the current ignition timing setting.

[0112] After calculating the energy transfer rate by heat transfer from the gas in the combustion chamber to the surface of the combustion chamber wall, which is required to maintain the surface temperature, in step S1502, the processing of the advance angular speed calculation unit 505 proceeds to step S1503. In step S1503, advance angle speed calculation unit 505 calculates the ignition timing that achieves the target energy transfer rate by heat transfer to the surface of the combustion chamber wall. For example, assuming that dQwall,tar / dt calculated in step S1202 is equal to the values ​​of Equation 2 and Equation 3, Equation 23 is derived.

[0113]

number

[0114] Here, θtar,a2 is the target ignition timing [deg]. By solving Equation 19 for θtar,a2, the target ignition timing is derived as shown in Equation 24.

[0115]

number

[0116] In step S1504, advance angle speed calculation section 505 converts the time required to converge to the target ignition timing into an advance angle speed θdot [s]. The advance angle speed is determined by the following equation (25).

[0117]

number

[0118] Note that the time it takes for the ignition timing to converge affects the knock frequency. Therefore, in this embodiment, the time tdel for the ignition timing to converge to the target ignition timing is set based on the time required to achieve the target knock frequency.

[0119] FIG. 16 is a diagram illustrating the relationship between the ignition timing convergence time and the knock frequency. The horizontal axis represents the ignition timing convergence time, and the vertical axis represents the knock frequency. When the operating conditions of the internal combustion engine ENG, such as the torque and rotation speed, are constant, the knock frequency decreases as the ignition timing convergence time increases. Therefore, in this embodiment, the ignition timing convergence time that results in a preset target knock frequency, as indicated by the dashed line, can be used as the target ignition timing convergence time tdel.

[0120] By determining the advance rate of the ignition timing as described above, advance rate calculation unit 505 can appropriately set the advance rate of the ignition timing in accordance with changes in the amount of heat conduction from the surface to the interior, which changes with changes in the internal temperature. As a result, advance rate calculation unit 505 can control the surface temperature to an appropriate temperature range while taking the internal temperature into consideration, thereby achieving both the suppression of knock recurrence and the suppression of deterioration in fuel economy due to retarding the ignition timing.

[0121] According to the internal combustion engine control device of this embodiment, when controlling the ignition timing after a knock occurs, the ignition timing can be controlled while appropriately managing the surface temperature of the combustion chamber at a temperature close to the knock recurrence temperature. Here, by taking the internal temperature into consideration, appropriate ignition retard amounts, advance amounts, and advance speeds can be set.

[0122] Fig. 17 shows the time change in an example of the operation of the ignition timing in this embodiment. Fig. 17(a) shows the case where the difference between the internal temperature and the surface temperature of the combustion chamber wall is small, and Fig. 17(b) shows the case where the difference between the internal temperature and the surface temperature of the combustion chamber wall is large. In this embodiment, when the internal temperature is high and the difference between the internal temperature and the surface temperature is small, the delay amount in the delay control and the advance amount in the first advance control can both be set larger than when the internal temperature is low and the difference between the internal temperature and the surface temperature is large.

[0123] Conversely, when the internal temperature is low and the difference between the internal temperature and the surface temperature is large, the delay amount in the delay control and the advance amount in the first advance control can both be set smaller than when the internal temperature is high and the difference between the internal temperature and the surface temperature is small. Therefore, the ignition timing control unit 502 of this embodiment can set the amount of retardation so that it has a negative correlation with the difference between the surface temperature and the internal temperature. Also, the ignition timing control unit 502 of this embodiment can set the amount of advancement so that it has a negative correlation with the difference between the surface temperature and the internal temperature.

[0124] Furthermore, in this embodiment, when the internal temperature is high and the difference between the internal temperature and the surface temperature is small, the advance time in the second advance control can be set longer than when the internal temperature is low and the difference between the internal temperature and the surface temperature is large. Therefore, the ignition timing control unit 502 of this embodiment can set the advance angle speed in the second advance angle control so that it has a positive correlation with the difference between the surface temperature and the internal temperature.

[0125] Therefore, the control device of this embodiment can appropriately suppress the recurrence of knock in various situations while controlling the ignition timing by avoiding excessive ignition timing retardation or an excessively long period of ignition timing retardation. As a result, it is possible to appropriately control the ignition timing while suppressing deterioration in efficiency, such as fuel economy and output, after the occurrence of knock during engine operation.

[0126] [Second embodiment] The second embodiment is an example in which the combustion chamber wall temperature is estimated by a process different from that of the first embodiment to control the ignition timing. Fig. 18 is a flowchart showing the processing for estimating the combustion chamber temperature based on the knock intensity and knock frequency. The processing described in Fig. 7 is an estimation method based on a physical formula. In Fig. 18, a combustion chamber wall temperature estimation unit 501 simply estimates the combustion chamber wall temperature based on the knock frequency and knock intensity.

[0127] In step S1801, the combustion chamber wall temperature estimation unit 501 calculates the knock frequency based on the knock flag. Here, the knock frequency is a value calculated based on the number of knocks that occurred in the most recent predetermined number of combustion cycles, and represents the number of knocks that occurred per combustion cycle. For example, it can be expressed as in Equation 26.

[0128]

number

[0129] For example, the combustion chamber wall temperature estimation unit 501 starts counting the number of combustion cycles when the engine load state reaches a preset condition under which knocking is expected to occur. After counting the number of knocks that have occurred in the combustion cycles up to just before the predetermined number of cycles is reached, when a knock flag for the predetermined number of combustion cycles is detected, the combustion chamber wall temperature estimation unit 501 can calculate the knock frequency based on the weighted average equation in Equation 26.

[0130] When the engine load condition reaches a preset condition, for example, when the condition is reached where knocking is not expected to occur, the combustion chamber wall temperature estimation unit 501 can stop or reset counting the number of combustion cycles. Furthermore, taking into consideration that the sum of the coefficients of R(k-1) and f(k) is 1, Equation 26 may be simplified and the knock frequency may be calculated using a weighted average equation such as Equation 27.

[0131]

number

[0132]

number

[0133] In this embodiment, instead of calculating the knock frequency based on the number of knocks that occurred in the most recent predetermined number of combustion cycles, the knock frequency may be calculated using a weighting value for a single detected knock flag. This eliminates the need to store the number of recent predetermined number of knocks. In this case, for example, the knock frequency when a knock flag is detected under various operating conditions is obtained in advance through simulation, experiment, or the like, and a weighting value for a single knock flag is set in advance using a weighted average.

[0134] Furthermore, by using the weighting value, when one knock flag is detected, for example, combustion chamber wall temperature estimation unit 501 can calculate the knock frequency from equation (29).

[0135]

number

[0136] Here, KFR is the knock frequency [-], KnockFlag is the knock flag [-], and is a flag that is set to 1 (True) when a knock occurs and 0 (False) when a knock does not occur. W is a preset weighting value for the weighted average, and is set between 0 and 1.

[0137] After calculating the knock frequency, the process of combustion chamber wall temperature estimation unit 501 proceeds to step S1802, where the surface temperature is estimated from the knock intensity. Fig. 19 is a schematic diagram showing a map illustrating the relationship between knock intensity and the surface temperature of the combustion chamber wall. As the surface temperature increases, the amount of unburned air-fuel mixture that auto-ignites increases, resulting in increased knock intensity. This relationship indicates that there is a positive correlation between knock intensity and surface temperature. By defining the relationship between knock intensity and surface temperature in advance through simulation or experiment, the surface temperature can be determined from the knock intensity while the internal combustion engine is operating.

[0138] Next, the processing of combustion chamber wall temperature estimation unit 501 proceeds to step S1803, where the difference between the internal temperature and surface temperature of the combustion chamber wall is estimated from the knock frequency. Figure 20 is a schematic diagram showing a map that shows the relationship between knock frequency and the difference between surface temperature and internal temperature. The difference between internal temperature and surface temperature can be obtained using this map. As shown in Figure 20, there is a negative correlation between knock frequency and the relationship between surface temperature and internal temperature.

[0139] The negative correlation between knock frequency and the difference between surface temperature and internal temperature can be explained as follows. As shown in Fig. 4, when the difference between the surface temperature and internal temperature is large, it takes longer for the surface temperature to reach a steady-state value than when the difference between the two is small. This change suggests that when the difference between the surface temperature and internal temperature is large, it takes longer for the surface temperature to reach the knock recurrence temperature than when the difference between the two is small, and the knock occurrence frequency decreases. In this way, it can be said that there is a negative correlation between knock frequency and the difference between the surface temperature and internal temperature.

[0140] Therefore, by specifying the relationship between the knock frequency and the difference between the surface temperature and the internal temperature in advance through simulations or experiments, as shown in Figure 20, the relationship between the surface temperature and the internal temperature can be obtained from the knock frequency that occurs during operation.

[0141] Next, the process of the combustion chamber wall temperature estimation unit 501 proceeds to step S1804, where the internal temperature of the combustion chamber wall is estimated. The internal temperature can be calculated from the sum of the surface temperature calculated in step S1802 and the difference between the surface temperature and the internal temperature calculated in step S1803.

[0142] After the combustion chamber wall temperature estimation unit 501 estimates the internal temperature of the combustion chamber wall, the ignition timing control unit 502 controls the ignition timing based on the estimated value. 21 is a flowchart showing the processing contents of the delay angle amount calculation unit, the advance angle amount calculation unit, and the advance angular speed calculation unit. The delay angle amount calculation unit 503 performs the processing of step S2101, the advance angle amount calculation unit 504 performs the processing of step S2102, and the advance angular speed calculation unit 505 performs the processing of step S2103.

[0143] That is, in step S2101, the retardation amount calculation unit 503 sets the retardation amount based on the surface temperature and the internal temperature. At this time, a map that has been previously adapted based on experiments or simulations can be used.

[0144] 22 is a schematic diagram showing a map of the ignition retard amount, with the surface temperature of the combustion chamber wall and the internal temperature as axes. The map of the ignition retard amount has a relationship in which the retard amount increases as the surface temperature increases, and also increases as the internal temperature increases.

[0145] In step S2102, advance amount calculation unit 504 calculates the ignition advance amount in the first advance control. The ignition advance amount is calculated by, for example, calculating the difference between the advance amount and the retard amount based on the surface temperature and the internal temperature using a map of the difference between the advance amount and the retard amount (the difference is 0 when returning to the ignition timing immediately before the ignition retard) that has been adapted in advance based on experiments or simulations, and then determining the ignition timing advance amount from the calculated value.

[0146] Fig. 23 is a map showing the difference between the retard and advance amounts, with the surface temperature and the difference between the surface and internal temperatures as axes. The lower the surface temperature, the smaller the difference between the retard and advance amounts, and the larger the difference between the surface and internal temperatures, the smaller the difference between the retard and advance amounts is set. The reason for this is that when the surface temperature is low, it can be assumed that there is a low probability that knock will recur even if the original ignition timing is returned to after the ignition retard.

[0147] Furthermore, if the difference between the surface temperature and the internal temperature is large (which is essentially the same as saying that the internal temperature is low), the surface temperature is unlikely to rise even if the original ignition timing is returned to after ignition retardation, and it can be assumed that the probability of knock recurring is low. When the difference between the retard angle amount and the advance angle amount is determined using the map in FIG. 23, the advance angle amount can be calculated by subtracting the difference between the retard angle amount and the advance angle amount determined using the map from the retard angle amount.

[0148] In step S2103, the advance angle speed calculation unit 505 calculates the ignition timing advance angle speed in the second advance angle control. The ignition timing advance angle speed can be calculated based on the difference between the surface temperature and the internal temperature. 24 is a schematic diagram showing the relationship between the difference between the surface temperature and the internal temperature of the combustion chamber wall and the advance angular speed. This relationship between the difference between the surface temperature and the internal temperature and the advance angular speed has been calculated in advance through experiments and simulations.

[0149] The greater the difference between the surface temperature and the internal temperature, the less likely it is that the surface temperature will rise, so the ignition timing can be returned earlier and the advance angle rate can be increased. On the other hand, the smaller the difference between the surface temperature and the internal temperature, the easier it is for the surface temperature to rise, and the condition for cooling the internal temperature becomes necessary, so the advance angular speed must be small. For this reason, the advance angular speed is set so that it has a positive correlation with the difference between the surface temperature and the internal temperature.

[0150] As with the first embodiment, the internal combustion engine control device of the second embodiment can appropriately control the ignition timing while suppressing deterioration in fuel economy and output efficiency after a knock occurs during engine operation. Moreover, in the second embodiment, the combustion chamber wall temperature estimation unit 501 simply estimates the combustion chamber wall temperature based on the knock intensity and knock frequency. Furthermore, the ignition timing control unit 502 uses maps to determine the retard amount in the retard control, the advance amount in the first advance control, and the advance rate in the second advance control. Therefore, the internal combustion engine control device of the second embodiment can easily appropriately control the ignition timing.

[0151] The above-described embodiments can be modified as appropriate within the scope of the claims of the present invention. For example, in each embodiment, ignition timing control unit 502 can estimate the state of fuel and reflect this in the operation of ignition timing. The state of fuel supplied to the engine (supplied fuel) can be estimated from the relationship between the estimated value of the surface temperature when knock occurred and the knock recurrence temperature.

[0152] For example, if the estimated surface temperature when knock occurs is higher than the knock recurrence temperature, it suggests that the supplied fuel is less likely to cause knock than the fuel used to predetermine the knock recurrence temperature. In this case, the greater the difference between the estimated surface temperature and the knock recurrence temperature, the less likely it is that knock will occur with the supplied fuel. Therefore, the ignition timing control unit 502 may correct the ignition retard amount set in each embodiment so that it has a negative correlation with this difference. Alternatively, the ignition timing control unit 502 may correct the advance amount set in each embodiment so that it has a positive correlation with this difference. In this way, the control device for an internal combustion engine in each embodiment can suppress excessive ignition retard and insufficient ignition advance, thereby suppressing deterioration in fuel economy and output efficiency.

[0153] Conversely, if the estimated surface temperature at the time of knock occurrence is lower than the knock recurrence temperature, this suggests that the supplied fuel is more likely to cause knock than the fuel used to predetermine the knock recurrence temperature. In this case, the greater the difference between the knock recurrence temperature and the estimated surface temperature, the more likely it is that knock will occur with the supplied fuel. Therefore, the ignition timing control unit 502 may correct the ignition retard amount set in each embodiment so that it has a positive correlation with this difference. Alternatively, the ignition timing control unit 502 may correct the advance amount set in each embodiment so that it has a negative correlation with this difference. In this way, the control device for an internal combustion engine in each embodiment can suppress insufficient ignition retard and excessive ignition advance, thereby suppressing deterioration in fuel economy and output efficiency.

[0154] Furthermore, in each of the above embodiments, an example has been described in which the operation of the ignition timing is started when the knock sensor 21 detects a knock flag, but this is not particularly limited. For example, it is also possible to detect a knock when the estimated value of the surface temperature of the combustion chamber wall or the estimated value of the internal temperature reaches a predetermined value, and have the ignition timing control unit start operating the ignition timing in the same way as when a knock flag is detected.

[0155] In this case, the predetermined value may be, for example, a value that includes a margin from the knock recurrence temperature. Furthermore, the operation of the ignition timing may be initiated when the difference between the estimated value of the combustion chamber wall surface temperature and the estimated value of the internal temperature reaches a predetermined value. Furthermore, the estimated values ​​of the surface temperature and internal temperature used in the processing from step S2101 to S2103 in the flow chart of FIG. 21 may be the surface temperature and internal temperature calculated in the flow chart of FIG. 18, or values ​​estimated using the flow chart of FIG. 7. [Explanation of symbols]

[0156] 1...Air flow sensor, 2...Electronically controlled throttle, 3...Intake pressure sensor, 5...Variable valve, 6...Collector, 7 Intake pipe, 9...Air-fuel ratio sensor, 10...Three-way catalyst, 11...External EGR section, 12...Accelerator opening sensor, 13...Fuel injection device (injector), 14...Cylinder, 15...Exhaust pipe, 16...Ignition coil, 17...Spark plug, 18...Temperature sensor, 19...Crank angle sensor, 20...Oil jet system, 20a...Oil pump, 100...ECU, 121...Input circuit, 122...Input / output port, 124...Ignition control section, 125...Fuel injection control section, 501...Combustion chamber wall temperature estimation section, 502...Ignition timing control section, 503...Retard amount calculation section, 504...Advance amount calculation section, 505...Advance speed calculation section, ENG...Internal combustion engine (engine)

Claims

1. a combustion chamber wall temperature estimation unit that calculates an estimated value of a combustion chamber wall temperature including a combustion chamber wall surface temperature and a combustion chamber wall internal temperature; an ignition timing control unit that retards the ignition timing and advances the ignition timing after the retardation, A control device for an internal combustion engine, wherein the ignition timing control unit, in retard control that performs the retard when knock is detected, sets the retard amount based on at least the estimated value of the temperature inside the combustion chamber wall.

2. 2. The control device for an internal combustion engine according to claim 1, wherein the ignition timing control unit sets the amount of retardation based on estimated values ​​of the combustion chamber wall surface temperature and the combustion chamber wall internal temperature.

3. 3. The control device for an internal combustion engine according to claim 2, wherein the ignition timing control unit sets the amount of retardation so that the amount of retardation has a negative correlation with a difference between the combustion chamber wall surface temperature and the combustion chamber wall internal temperature.

4. 2. The control device for an internal combustion engine according to claim 1, wherein the ignition timing control unit, in advance control for advancing the ignition timing after the retardation, sets an advance amount based on at least the estimated value of the temperature inside the combustion chamber wall.

5. 5. The control device for an internal combustion engine according to claim 4, wherein the ignition timing control unit sets the advance amount based on estimated values ​​of the combustion chamber wall surface temperature and the combustion chamber wall internal temperature.

6. 6. The control device for an internal combustion engine according to claim 5, wherein the ignition timing control unit sets the advance amount so that the advance amount has a negative correlation with a difference between the combustion chamber wall surface temperature and the combustion chamber wall internal temperature.

7. 5. The control device for an internal combustion engine according to claim 4, wherein in the advance angle control, an advance angle speed is set based on at least the estimated value of the temperature inside the combustion chamber wall.

8. 8. The control device for an internal combustion engine according to claim 7, wherein in the advance control, the advance speed is set based on the estimated value of the combustion chamber wall surface temperature and the estimated value of the combustion chamber wall internal temperature.

9. 9. The control device for an internal combustion engine according to claim 8, wherein the ignition timing control unit sets the advance angular speed so as to have a positive correlation with a difference between the combustion chamber wall surface temperature and the combustion chamber wall internal temperature.

10. When the estimated value of the combustion chamber wall surface temperature reaches a predetermined value, the ignition timing control unit 10. The control device for an internal combustion engine according to claim 1, wherein the ignition timing is retarded by a predetermined retard amount and then advanced by a predetermined advance amount.

11. 10. The control device for an internal combustion engine according to claim 1, wherein the retard amount is set based on a retard target surface temperature that is a predetermined retard margin from a knock recurrence temperature.

12. 10. The control device for an internal combustion engine according to claim 4, wherein the advance amount is set based on an advance target surface temperature that is a predetermined advance margin from a knock recurrence temperature.

13. The ignition timing control unit a retard control for retarding the ignition timing; a first advance control for advancing the ignition timing by an angle smaller than the amount of delay in the retard control immediately after the retard control; 10. The control device for an internal combustion engine according to claim 4, further comprising: a second advance control for advancing the ignition timing at an advance rate slower than that of the first advance control immediately after the first advance control.

14. 10. The control device for an internal combustion engine according to claim 1, wherein the combustion chamber wall temperature estimation unit estimates the combustion chamber wall surface temperature based on at least a knock intensity, and estimates the combustion chamber wall internal temperature based on at least a knock frequency.

15. a plurality of estimated knock occurrence temperatures under predetermined operating conditions and the retard amount at each estimated knock occurrence temperature among the plurality of estimated knock occurrence temperatures are set in advance, The ignition timing control unit when the estimated value of the combustion chamber wall temperature when the knock is detected is higher than the assumed knock occurrence temperature under the operating conditions when the knock is detected, the retard amount is set so as to have a negative correlation with the difference between the estimated value and the assumed knock occurrence temperature, or the advance amount is set so as to have a positive correlation with the difference between the estimated value and the assumed knock occurrence temperature; 10. The control device for an internal combustion engine according to claim 1, wherein, when the estimated value of the combustion chamber wall temperature when the knock is detected is lower than the assumed knock occurrence temperature under the operating conditions when the knock is detected, the retard amount is set so as to have a positive correlation with the difference between the estimated value and the assumed knock occurrence temperature, or the advance amount is set so as to have a negative correlation with the difference between the estimated value and the assumed knock occurrence temperature.

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